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Physical Layer Security in Lossy Untrusted Relay Networks with Finite Blocklength

Shen Qian, Meng Cheng

Published Jan 10, 2025• 1 citation

Abstract

In this paper, we examine the physical layer security (PLS) in lossy untrusted relay networks, focusing on finite blocklength transmissions. In such networks, ensuring secure communication is particularly challenging due to the presence of untrusted relay nodes and the inherent limitations of short-packet transmissions. We propose the reliable-and-secure probability (RSP) as a performance metric to evaluate the likelihood that the destination node successfully recovers the transmitted message while untrusted relays experience an outage. Two basic network topologies are taken into consideration, which are the three-node one way network and the single-source multi-untrusted-relay network without direct source-to-destination link. By optimizing power allocation and relay positioning, the RSP can be significantly improved, even when decoding errors occur at the relays. The study demonstrates that lossy decode-and-forward relaying complicates secure communication but also presents opportunities for performance enhancement through careful resource management. Numerical simulations validate the effectiveness of the proposed optimization strategies in enhancing security, especially for applications in ultra-reliable low-latency communication and massive machine-type communication in 5G/6G networks. Future research will focus on deriving more precise closed-form expressions for RSP in finite blocklength settings and investigating machine learning-based approaches for real-time optimization of secure communications in dynamic wireless environments. This study contributes to the growing body of knowledge on PLS in modern wireless systems, offering insights for future advancements.

DOI: 10.69709/coconnect.2024.003818

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In this paper, we examine the physical layer security (PLS) in lossy untrusted relay networks, focusing on finite blocklength transmissions. In such networks, ensuring secure communication is particularly challenging due to the presence of untrusted relay nodes and the inherent limitations of short-packet transmissions. We propose the reliable-and-secure probability (RSP) as a performance metric to evaluate the likelihood that the destination node successfully recovers the transmitted message while untrusted relays experience an outage. Two basic network topologies are taken into consideration, which are the three-node one way network and the single-source multi-untrusted-relay network without direct source-to-destination link. By optimizing power allocation and relay positioning, the RSP can be significantly improved, even when decoding errors occur at the relays. The study demonstrates that lossy decode-and-forward relaying complicates secure communication but also presents opportunities for performance enhancement through careful resource management. Numerical simulations validate the effectiveness of the proposed optimization strategies in enhancing security, especially for applications in ultra-reliable low-latency communication and massive machine-type communication in 5G/6G networks. Future research will focus on deriving more precise closed-form expressions for RSP in finite blocklength settings and investigating machine learning-based approaches for real-time optimization of secure communications in dynamic wireless environments. This study contributes to the growing body of knowledge on PLS in modern wireless systems, offering insights for future advancements.

This paper investigates the physical layer security performance of an untrusted relay network in the finite blocklength regime. Lossy decode-and-forward (DF) relaying is considered at the untrusted relay. Different from conventional DF relaying, the relay always forwards information sequences to the destination even if error is detected at the relay, which can be utilized to enhance the security of the untrusted relay network. Based on the characteristics of short-packet communications, the reliable-and-secure probability is proposed and numerically derived for evaluating the security performance in the physical layer of the untrusted relay network. Reliable-and-secure probability represents the probability that the destination can recover the original message sent from the source, whereas the relays cannot. It is found that as long as the contribution of the transmit power of source and relays is balanced, a certain degree of reliable-and-secure probability can be held for short-packet communications in the untrusted relay network.

A two-untrusted-relay transmission scheme is proposed with lossy-forward (LF) relaying being utilized. Two untrusted relays are located between one source and one common destination and there is no direct link between the source and the destination, which referred to as diamond relaying network. Since LF relaying allows intra-link errors and always forwards the decoded information sequences from the relays to the destination, it realizes the reliable and secure transmission of decoder-and-forward based relay networks with untrusted relays. Reliable-and-secure probability is derived to evaluate the performance of the untrusted relay networks, which represents the probability that the destination can recover the original message sent from the source whereas the relays cannot. We find that as long as the contributions of the transmit power of source and relays are balanced, a certain degree of reliable-and-secure probability can be held, even without the support from a friendly jamming signal.

In this paper, we investigate the physical layer security performance of untrusted decode-and-forward (DF) relay networks allowing intra-link errors with cooperative jamming. Different from traditional DF relaying protocol, the decoded message at the relay will always be forwarded to the destination node in decode-and-forward relaying allowing intra-link errors (DF-IE), which can be leveraged to enhance the security of relay networks with untrusted relays. To further improve the security performance of DF-IE, we allow the destination node to send jamming signals to impair the signal reception at the relay node, which is referred to as DF-IE with cooperative jamming (DF-IE-CJ). Reliable-and-secure probability (RSP) is used to evaluate the performance of the untrusted relay networks, which represents the probability that the destination node can successfully decode the original message sent from the source node while the relay node can not decode the original message. First, the RSP of DF-IE-CJ is derived from a fading scenario where all the channels between the nodes suffer from block Rayleigh fading. Next, we propose a power allocation scheme to maximize the RSP with different signal-to-noise ratios (SNRs). To verify the effectiveness of DF-IE-CJ, we compare the RSP performance of DF-IE-CJ with that of a widely used schemes, cooperative jamming (CJ). A series of numerical simulations verified the accuracy of the theoretical analysis, and the superiority of DF-IE-CJ over CJ about 5% in RSP.

This work explores the impact of optimal power allocation on the physical layer security of lossy decode-and-forward untrusted relay networks using Alamouti Space-Time Block Code (STBC). We introduce the reliable-and-secure probability (RSP) metric to measure the likelihood of successful message recovery at the destination while ensuring the message remains unintelligible to the relays. In high spectral efficiency scenarios, allocating more power to the untrusted relay significantly enhances the RSP, surpassing low spectral efficiency results. A balanced power allocation between the source and the relay, with Alamouti STBC, achieves a high RSP. However, the peak RSP is achieved when the power contributions from the source and the relay are balanced.

This paper tackles the challenge of secure and reliable data transmission in diamond network configurations featuring two untrusted relays with low-security clearance. We propose an innovative approach that employs lossy-decode and -forward relaying at these untrusted relays to boost transmission reliability while safeguarding the source information from potential eavesdroppers. An essential contribution of this work is the introduction of the reliable and secure probability (RSP) metric. This metric assesses the likelihood of the destination successfully retrieving the original information while maintaining its confidentiality from untrusted relays. Our analysis shows that the integration of cooperative jamming signals markedly enhances the RSP, resulting in superior security and reliability. Simulation results confirm that optimal power distribution among the source, relays, and destination further maximizes the RSP. These findings underscore the effectiveness of our proposed scheme in ensuring secure and reliable communication in environments with untrusted relays, suggesting its potential as a robust solution for secure communications in diamond network configurations.

This letter considers a diamond network with two untrusted relays with low-security clearance level. Lossy decoder-and-forward is utilized at both the untrusted relays to enhance the reliability of transmission and to keep the source information confidential to the untrusted relays. The reliable-and-secure probability (RSP), which is the probability that the original messages can be retrieved at the destination while keeping confidential to the relays, is derived. It is found that with the help of cooperative jamming signal, superior reliability and security performance in terms of RSP can be achieved.